1. Field of Invention
The invention relates to fluid ejection systems that use microwave dryers.
2. Description of Related Art
A fluid ejection system, such as an ink jet printer, typically has at least one printhead from which droplets of fluid are directed towards a recording medium or recording sheet. Within the printhead, the fluid is contained in a plurality of channels. Droplets of the fluid are expelled as required from orifices or nozzles located at the end of the channels.
A fluid ejector head may be incorporated into either a carriage type fluid ejection system, a page-width type fluid ejection system, or a combination of the two. The carriage type fluid ejection system typically has a relatively small fluid ejector head containing the fluid channels and nozzles. The fluid ejector head is often sealingly attached to a disposable fluid supply cartridge. The combined fluid ejector head and cartridge assembly is attached to a carriage, which is reciprocated to eject fluid according to one swath of information at a time on a receiving medium. After the swath is formed, the receiving medium is stepped a distance equal to the height of the swath, or a portion of the swath, so that the next swath overlaps or is contiguous with the previous swath. The procedure is repeated until all of the information has been used. In contrast, the page-width fluid ejection system includes a fluid ejector head having a length sufficiently long to eject fluid across the width or length of the receiving medium. The receiving medium is continually moved past the page-width fluid ejector head in a direction normal to the length of the fluid ejector head and at a constant or varying speed during the fluid ejection process.
Many fluids, particularly those used in ink jet printing, include a colorant and a liquid. Some fluids also include a low vapor pressure solvent. When fluid is ejected onto the receiving medium, the individual spots of fluid deposited on the receiving medium form a desired pattern. Once deposited, the liquid is removed from the fluid to leave a desired residue.
Liquid can be removed from the fluid and the receiving medium by a number of methods. One simple method is natural air drying, in which the liquid component of the fluid deposited on the receiving medium is allowed to evaporate without mechanical assistance. A significant amount of fluid is diffused and absorbed into the receiving medium when this method is used. In high-speed page-width fluid ejection systems, drying is usually achieved by transporting the receiving media through a microwave dryer to evaporate the liquid from the fluid.
Microwave dryers are particularly efficient for drying fluid on receiving media in high speed thermal ink jet printing. However, introducing foreign metallic materials, such as, for example, staples, paper clips, decorative metallic leaf on letterhead and the like, into a microwave dryer cavity can have damaging consequences when the dryer is generating electromagnetic waves. Any metal entering the microwave dryer cavity under these conditions will immediately couple microwave power. This causes the metal to heat up dramatically and to arc and possibly damage the microwave dryer. Receiving media and transport belts in close proximity to the metal and the arc will rapidly heat up and deform. Damage to transport belts can affect the output quality of the fluid receiving medium, affect the reliability of the entire fluid ejection system and frustrate the user. Further, electromagnetic coupling results in electromagnetic radiation from the cavity of the microwave dryer which is a safety hazard. Preventing this problematic scenario requires assuring that foreign metallic materials cannot enter the microwave dryer cavity when microwave RF power is applied.
This invention provides systems and methods that detect metallic materials during feeding recording media to the ejection area of the fluid ejection system.
This invention separately provides systems and methods that reduce damage to a microwave dryer by stopping feeding operations upon detecting offending materials and allowing the removal of the offending materials.
This invention separately provides systems and methods that detect metallic materials prior to entry of such metallic materials into a microwave dryer.
This invention additionally provides systems and methods that reduce damage by turning off microwave power when metallic materials are detected in this manner.
This invention separately provides systems and methods that detect metallic materials after the offending materials exit from a microwave dryer and to turn on microwave power after the metallic materials exit the microwave dryer cavity.
These and other features and advantages of this invention are described in, or are apparent from, the following detailed description of various exemplary embodiments of the systems and methods according to this invention.